arXiv subjects

Bogdan A. Pastrav

Publications and source records attributed to Bogdan A. Pastrav.

8 recordsLinked to original sources

arXiv2025

The relations between dust properties and galaxy global / integrated quantities in the nearby Universe

Results of a case study of a sample of low-redshift galaxies are presented, to determine dust temperatures and emissivity indices through a less time-consuming method, and to connect both global and integrated galaxy properties with those of dust, ISM and star-formation. Dust temperatures ($T_{d}$) are determined based on the corresponding galaxy dust masses, independently calculated in our previous work, through a self-consistent method, without the need to actually perform a complete spectral energy distribution (SED) fit of the cold dust emission fluxes. The range and average dust temperatures are found to be consistent within errors with values from other studies. Simultaneously, the dust emissivity indices ($β_{d}$) are determined, and their evolution with temperature quantified, with the $T_{d}$ anti-correlation still being present. It is investigated whether $β_{d}$ can be predicted from other relation or if it scales with other integrated dust / ISM or galaxy property, which could be used as a proxy. In this respect, new and established relations between $T_{d}$, $β_{d}$, the dust surface density and global / integrated galaxy and star-formation related quantities are presented and analysed. We find that SFR, sSFR or $Σ_{SFR}$ are inconclusive traces of the dust temperature. We also find that the extent of dust emission distribution is slightly lower on average, but comparable with the optical stellar continuum emission one. The results and conclusions can be relevant for larger scales studies of low to mid-redshift galaxies from the latest surveys.

astro-ph.GA↗

arXiv2023

Dust and inclination corrected star-formation and interstellar medium scaling relations in nearby galaxies

Following from our recent work, we present a detailed analysis of star-formation and interstellar medium (ISM) scaling relations, done on a representative sample of nearby galaxies. H$α$ images are analysed in order to derive the integrated galaxy luminosity, known as a more instantenous and accurate star-formation rate (SFR) tracer, and the required photometric and structural parameters. Dust and inclination corrected H$α$ luminosities, SFRs and related quantities are determined using a self-consistent method based on previous work prescriptions, which do not require the assumption of a dust attenuation curve and use of Balmer decrements (or other hydrogen recombination lines) to estimate the dust attenuation, with the advantage of determining dust opacities and dust masses along the way. We investigate the extent to which dust and inclination effects bias the specific parameters of these relations, the scatter and degree of correlation, and which relations are fundamental or are just a consequence of others. Most of our results are consistent within errors with other similar studies, while others come in opposition or are inconclusive. By comparing the B band optical and H$α$ (star-forming) discs scalelengths, we found on average, the star-formation distribution to be more extended than the stellar continuum emission one (the ratio being 1.10), this difference increasing with stellar mass. Similarly, more massive galaxies have a more compact stellar emission surface density than the star-formation one (average ratio of 0.77). The method proposed can be applied in larger scale studies of star-formation and ISM evolution, for normal low to intermediate redshift galaxies.

astro-ph.GA↗

arXiv2022

Intrinsic dust and star-formation scaling relations in nearby galaxies

Following from our recent work, we present results of a detailed analysis of a representative sample of nearby galaxies. The photometric parameters of the morphological components are obtained from bulge-disk decompositions, using GALFIT software. The previously obtained method and library of numerical corrections for dust, decomposition and projection effects, are used to correct the measured (observed) parameters to intrinsic values. Observed and intrinsic galaxy dust and star-formation related scaling relations are presented, to emphasize the scale of the biases introduced by these effects. To understand the extent to which star-formation is distributed in the young stellar disks of galaxies, star-formation connected relations which rely on measurements of scale-lengths and fluxes / luminosities of H$α$ images, are shown. The mean dust opacity, dust-to-stellar mass and dust-to-gas ratios of the sample, together with the main characteristics of the intrinsic relations are found to be consistent with values found in the literature.

astro-ph.GA↗

arXiv2021

On the scaling relations of bulges and early-type galaxies

Following from our recent work, we present here a detailed structural analysis of a representative sample of nearby spiral and early-type galaxies taken from the KINGFISH/ SINGS survey. The photometric parameters of bulges are obtained from bulge-disc decompositions using GALFIT data analysis algorithm. The method and corrections for projection and dust effects previously obtained are used to derive intrinsic photometric and structural bulge parameters. We show the main bulge scaling relations and the black hole relations, both observed and intrinsic ones, in B band. We find dust and inclination effects to produce more important changes in the parameters of the Kormendy relation for spiral galaxies, with the respective bulges of late-type galaxies residing on a steeper slope relation that the early-type galaxies. We observe that the Kormendy relation in combination with a bulge Sérsic index ($n_{b}$) threshold, does not produce a conclusive morphological separation of bulges. The $n_{b}$- bulge-to-total flux ratio ($B/T$) and $B/T$-stellar mass could be used to discriminate between late-type and early-type galaxies, while a further use of these parameters to divide bulges with different morphologies is problematic due to overlaps in the two distributions or large spread in values. We confirm the existence of two distinct intrinsic relations between the bulge luminosity (or absolute magnitude) and Sérsic index for late- and early-type galaxies, while the relations between the black-hole mass ($M_{BH}$) and bulge luminosity are not found to be statistically different at p<0.05. Within errors, we find statistically similar intrinsic $M_{BH}-n_{b}$ relations for all bulges.

astro-ph.GA↗

arXiv2020

The dust effects on galaxy scaling relations

Accurate galaxy scaling relations are essential for a successful model of galaxy formation and evolution as they provide direct information about the physical mechanisms of galaxy assembly over cosmic time. We present here a detailed analysis of a sample of nearby spiral galaxies taken from the KINGFISH survey. The photometric parameters of the morphological components are obtained from bulge-disk decompositions using GALFIT data analysis algorithm, with surface photometry of the sample done beforehand. Dust opacities are determined using a previously discovered correlation between the central face-on dust opacity of the disk and the stellar mass surface density. The method and the library of numerical results previously obtained are used to correct the measured photometric and structural parameteres for projection (inclination), dust and decomposition effects in order to derive their intrinsic values. Galaxy disk scaling relations are then presented, both the measured (observed) and the intrinsic (corrected) ones, in the optical regime, to show the scale of the biases introduced by the aforementioned effects. The slopes of the size-luminosity relations and the dust vs stellar mass are in agreement with values found in other works. We derive mean dust optical depth and dust/stellar mass ratios of the sample, which we find to be consistent with previous studies of nearby spiral galaxies. While our sample is rather small, it is sufficient to quantify the influence of galaxy environment (dust, in this case) when deriving scaling relations.

astro-ph.GA↗

arXiv2013

The effects of dust on the photometric parameters of decomposed disks and bulges

We present results of a study to quantify the effects of dust on the derived photometric parameters of disk and bulges obtained from bulge-disk decomposition: scale-length, effective radius, Sersic index, disk axis-ratio, and bulge-to-disk ratio. The dust induced changes in these parameters were obtained by fitting simulated images of composite systems (containing a disk and a bulge) produced using radiative transfer calculations. The simulations were fitted with the GALFIT 3.0.2 data analysis algorithm. Fits were done with both a combination of an exponential plus a variable-index Sersic function as well as with a combination of two variable-index Sersic functions. We find that dust is biasing the derived exponential scale-length of decomposed disks towards smaller values than would be otherwise derived if the galaxy were to have no bulge. Similarly, the derived bulge-to-disk ratio is biased towards smaller values. However, the derived axis-ratio of the disk is not changed in the decomposition process. The derived effective radius of decomposed disks of systems having exponential bulges is found to be less affected by dust when fits are done with two variable-index Sersic functions. For the same type of fits dust is found to bias the value of the derived effective radius of decomposed disks towards lower values for systems having de Vaucouleurs bulges. All corrections derived in this paper are made available in electronic form.

astro-ph.CO↗

arXiv2013

The effects of dust on the derived photometric parameters of disks and bulges in spiral galaxies

We present results of a study to quantify the effects of dust on the derived photometric parameters of disks (old stellar disks and young stellar disks) and bulges: disk scale-lengths, axis-ratios, central surface-brightness, bulge effective radii and Sersic indexes. The changes in the derived photometric parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting simulated images of disks and bulges produced using radiative transfer calculations and the model of Popescu et al. (2011). The fits to the simulations were performed using GALFIT 3.0.2 data analysis algorithm and the fitted models were the commonly used infinitely thin disks described by exponential, general Sersic and de Vaucouleurs distributions. We find the young stellar disks to suffer the most severe variation in the photometric parameters due to dust effects. In this context we also present corrections for narrow line (Balmer line) images. Old stellar disks are also significantly affected by dust, in particular when fits are performed with exponential functions. The photometric parameters of bulges are to a lesser extent affected by dust. We also find that the variation of dust corrections with face-on dust opacity and inclination is similar for bulges with different intrinsic stellar emissivities (different Sersic index), with differences manifesting only close to edge-on orientations of the disk. Dust corrections for bulges are found to be insensitive to the choice of the truncation radius and ellipticity of the bulge. All corrections are listed in the Appendix and made available in electronic format.

astro-ph.CO↗

arXiv2012

Dust effects on the derived Sersic indexes of disks and bulges in spiral galaxies

We present a theoretical study that quantifies the effect of dust on the derived Sersic indexes of disks and bulges. The changes in the derived parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting Sersic distributions on simulated images of disks and bulges produced using radiative transfer calculations and the model of Popescu et al. 2011. We found that dust has the effect of lowering the measured Sersic index in most cases, with stronger effects for disks and bulges seen through more optically thick lines of sight.

astro-ph.GA↗